The aim of this research is to determine whether carotid body receptors mediated hypoxic insomnia. I have shown previously that the sleep cycle of rats is disrupted by exposure to 10 percent and this effect is primarily due to low rather than to associated hyperventilation or hypocapnia. If equivalent hypoxia caused by carbon monoxide fails to affect the sleep cycle this would be presumptive evidence that the insomnia of altitude is mediated by preripheral chemoreceptors. After completion of CO experiments, a comparable series of measurements will be carried out on rats or rabbits with surgically denervated carotid bodies. Rats will be provide with implanted electrodes to enable polygraphic recording of sleep states. Each rat will be subjected to 8 hour recording sessions within a "Flow-Through Fenn Box". This apparatus allows simultaneous recording of tidal volume, respiratory frequency, gas exchange and sleep states while breathing different gas mixtures. Sleep and respiration will be studies while breathing air, 10 percent or sufficient CO to produce 50 percent HbCO. The effects of hypoxia on duration and quality of sleep are of importance to high altitude physilogy as well as to the understanding of clinical disorders of sleep and breathing. The experiments proposed in this application may be expected to provide new information on the mechanism of hypoxic insomnia.